Hey guys, thanks for feedback...
However, I might add that I have the PS 3 since only ~2-3 weeks and therefore there shouldn't be all to much dust collecting into it... Also, it stands in the open and shouldn't have any trouble getting the air-circulation it needs.
It seems to me that the time-distances as to when all this happenes are quite constant, therefore I'll try to measure them and post them here; I might also add a video of how "loud" my PS 3 is. If I use this fine piece of hardware I often use it for 3 hours straight and it never once locked up until now
However, thanks for the repsonses so far, I'm happy for every other statment you guys have for me. If nothing helps I guess I'll just try and blow out those holes; maybe it really is dusty already...
@foss: Yea, I felt that too, guess the PS 3 rather puts out the hot air on it's right side or top (depending on how it's standing) instead of the back (it get's a bit hot there too, but no comparsion to the place you mentioned